EP1844744A1 - Laser arrangement for ophthalmic surgery - Google Patents

Abstract

The laser apparatus (12), for ophthalmic surgery e.g. laser assisted in situ keratomileusis (LASIK), has a pulsed laser unit (14) with an applicator (18) to direct the laser beam at the cornea of the eye (10), fixed in position by the vacuum in a suction chamber (20). The applicator incorporates an applanation lens (22) with a contact surface (24) and drives (25,26) to move the lens over the eye surface.

Description

The invention relates to a laser device for ophthalmological surgery, with a laser radiation source providing pulsed laser radiation and means for coupling the laser radiation into an ocular treatment site, wherein the coupling means comprise an applanation lens to be placed on an eye surface.

Pulsed laser radiation is used in ophthalmic surgery, for example, to apply corneal (corneal) incisions or to ablate (ablate) material from the surface of the cornea. The irradiated laser radiation causes a photodisruptive process in the corneal tissue, which leads to tissue separation or to the evaporation of tissue material. Such treatments of the cornea take place, for example, in the context of refractive methods for the reduction or complete correction of refractive errors of the eye, in which the cornea is reshaped and thereby its refractive properties are changed.

One of several common refractive procedures of corneal surgery is the so-called LASIK (Laser Keratomileusis). Here, a lid is cut out of the corneal epithelium either mechanically (by means of an oscillating cutting blade in a so-called microkeratome) or optically (by means of laser radiation), which still hangs on the cornea in part of its edge. Subsequently, this lid, usually referred to as a flap, is folded to the side, whereby the underlying stroma becomes accessible. With laser radiation stromal tissue is then removed in accordance with a previously determined for each patient ablation. The flap is then folded back, allowing the wound to heal relatively quickly.

Depending on the type of processing (eg incision or ablation) and / or tissue type, laser radiation of different wavelengths and / or pulse durations is used in laser-optical eye surgery. For the attachment of cuts in the cornea (for example for the preparation of a flap), for example, it is customary to use laser radiation in the low infrared (NIR) wavelength range, for example between 1000 and 1100 nm, with pulse durations in the femtosecond range or in the low picosecond range. In contrast, for the photoablation of stromal tissue usually laser radiation in the ultraviolet wavelength range, for example 193 nm or 347 nm, the pulse durations used can also be longer, down to the nanosecond range.

For a precise coupling of the laser radiation in the eye, it is known to fix the eye by means of a fixation device, which is sucked by vacuum on the eye. The fixation device comprises an applanation lens which serves as a distal coupling element for the laser radiation and which comes to sit in direct contact with the ocular surface when the fixation device is aspirated. The applanation lens creates a defined, stable interface between the eye and the laser system. Examples of fixation devices and applanation lenses can be found in US 2002/0103481 A1 . EP 0 608 052 A2 . EP 0 993 814 A1 and US 5,549,632 ,

Previous applanation lenses extend over large areas of the cornea and sit unmoving on the cornea. They are available in many different forms. By sucking the fixation device, they are pressed against the eye so that the cornea deforms and clings flat to the lens. Particularly in the case of plane-parallel applanation lenses and convexly curved lenses, a comparatively high biomechanical load is exerted on the cornea. In addition, the intraocular pressure is comparatively greatly increased by the deformation of the eye. There are also known applanation lenses with a concave, rotationally symmetrical contact surface on their side facing the eye, both with spherical and with aspheric curvature. Although the biomechanical loading of the cornea and the increased intraocular pressure can be alleviated with both concave lens variants. However, further improvements are needed in this regard.

The object of the invention is therefore to specify geometries for applanation lenses, which allow a further reduction of the intraocular pressure and the corneal load.

To solve this problem, it is provided according to one aspect of the invention in a laser device of the generic type described above that the applanation lens has an at least approximately bitorische contact surface on its side facing the eye. In another aspect, the applanation lens is configured as a rod lens, wherein the applanation lens is associated with movement drive means for moving the applanation lens over the ocular surface.

The first aspect makes use of the knowledge that the corneal surface of the human eye is not rotationally symmetrical but has different curvature along different meridians. In particular, the corneal surface can be modeled in good approximation and with good generality by a bitoric surface which has different radii of curvature in two mutually perpendicular meridian sections and is aspheric in both meridian directions. In the article " Custom photorefractive keratectomy of sperical and cylindrical refractive error and higher-order aberration "by Jim Schwiegerling and Robert W. Snyder, published in J. Opt. Soc. Am. A, Vol. 15, No. 9, September 1998, pages 2572- 2579 , a mathematical formula (there equation (6)) is given for describing a bitoric surface in polar coordinates. The contact surface of the applanation lens according to the invention can be modeled, for example, this formula. It is understood that the contact surface of the applanation lens does not have to be exactly bitoric in the strictly mathematical sense as long as it has aspherical contours with different radii of curvature in two transverse (not necessarily exactly perpendicular) meridional directions. The contact surface of the applanation lens may, for example, be formed on the basis of data obtained by measuring the corneal surface of one or more persons. Thus, for example, the applanation lens can be made individually for each patient or the data of a large number of persons can be converted into one or more standard lenses.

Due to the better adaptation of the contact surface of the lens to the actual shape of the corneal surface, the cornea must deform less so as to conform perfectly to the contact surface. Therefore, their biomechanical load is lower and also the intraocular pressure does not increase so much.

According to the second aspect, the applanation lens used is a rod lens which can be moved over the cornea by means of its associated movement drive means. The movable support allows the rod lens to be in contact with the ocular surface only in a relatively small local area. By moving the rod lens over the cornea, a larger area of the eye surface can be swept over, so that even with a rod lens larger areas of the eye, especially the cornea, can be processed. The small-surface contact with the ocular surface leads to the fact that the cornea is only locally deformed and loaded, which has a favorable effect on the total biomechanical load of the cornea and the intraocular pressure.

The movement driving means may be adapted to move the rod lens transversely to its longitudinal direction substantially linearly over the cornea. Alternatively or additionally, they may be adapted to rotate the rod lens about a lens vertical axis in order thereby to be able to cover larger areas of the corneal surface.

When viewed in a section transverse to the rod longitudinal direction, the rod lens preferably has a convexly rounded contact surface for the abutment with the cornea. The curvature of this contact surface may be spherical or aspherical. When viewed along the rod longitudinal direction, the contact surface of the lens may be substantially rectilinear. It is of course not excluded that the contact surface of the rod lens is concavely curved in view of the curvature of the corneal surface when viewed along its rod longitudinal direction, for example in at least approximately correspondence to the curvature of the corneal surface in one of the two main meridian directions.

The invention further provides an applanation lens for use in a laser device according to one of the above-described two modes. In this case, the applanation lens has an at least approximately bitoric contact surface or, in the case of a design as a rod lens, a convex-cylindrical contact surface on a lens side intended for contact with an ocular surface. Based on empirical data that can be obtained by surveying the corneal surface of a large number of individuals, it is possible to make a set of applanation lenses that differ in their radii of curvature and / or different asphericities of their interface.

• Figur 1 in starker schematischer Vereinfachung eine Lasereinrichtung für die ophthalmologische Chirurgie,
• Figur 2 schematisch die menschliche Hornhautoberfläche,
• Figur 3 im Schnitt und schematisch eine auf ein Auge aufgesetzte bitorische Applanationslinse gemäß einem Ausführungsbeispiel,
• Figur 4 eine Schnittansicht der Applanationslinse der Figur 3 entlang der dortigen Schnittrichtung IV-IV,
• Figur 5 im Schnitt schematisch eine auf ein Auge aufgesetzte Stablinse gemäß einem Ausführungsbeispiel,
• Figur 6 in schematischer Draufsicht eine linear über eine Hornhautoberfläche bewegte Stablinse und
• Figur 7 in schematischer Draufsicht eine durch Drehung über eine Hornhautoberfläche bewegbare Stablinse.

The invention will be further explained with reference to the accompanying drawings. They show:

• FIG. 1 shows a highly schematic simplification of a laser device for ophthalmological surgery,
• FIG. 2 schematically shows the human corneal surface,
• FIG. 3 in section and schematically a bitoric applanation lens applied to an eye according to an embodiment,
• FIG. 4 shows a sectional view of the applanation lens of FIG. 3 along the sectioning direction IV-IV there,
• FIG. 5 is a schematic sectional view of a rod lens mounted on an eye according to an exemplary embodiment;
• FIG. 6 is a schematic plan view of a linear lens moved over a corneal surface and FIG
• FIG. 7 is a schematic plan view of a rod lens which can be moved by rotation over a corneal surface.

Reference is first made to FIG. There, a human eye 10 is schematically indicated, the cornea is processed with a laser device 12, for example, to produce a flap section in the context of a LASIK treatment. The laser device 12 comprises a laser radiation source 14, which generates pulsed laser radiation in the NIR or UV wavelength range. Preferably, the pulse duration of the laser radiation generated is in the range of femtoseconds, but it can also be in the pico or even in the nanosecond range. The laser radiation source 14 may include, for example, a fiber laser, a solid-state laser or an excimer laser. Limitations on the type of the laser radiation source 14, the wavelength of the laser radiation generated by it and the pulse lengths are not intended in the context of the invention.

The radiation pulses provided by the laser radiation source 14 are conducted via a beam guiding arrangement 16 to a coupling-in unit 18, by means of which the pulses are coupled into the cornea of the eye 10. The coupling-in unit 18 comprises fixing means by means of which the coupling-in unit 18 or at least one eye-near part thereof can be fixed to the eye 10 by vacuum suction. For this purpose, the fixing means have a preferably annular suction chamber 20, which is closed when placing the coupling unit 18 on the eye 10 through the eye surface and is connected in a manner not shown to a vacuum pump. The fixation of the eye by suction of a fixation component is known per se in the art, which is why details of the fixation means of the coupling-in unit 18 need not be discussed here.

The beam guiding arrangement 16 or / and the coupling-in unit 18 furthermore contain deflection means (usually referred to as scanners), not shown in more detail, in order to prevent the Laser radiation over a target area to be processed to move away, and focusing means for focusing the injected into the eye 10 radiation to a target point (focus). Such deflecting and focusing means are well known in the art. A more detailed description of these components can therefore be omitted here.

As a distal coupling element, the coupling-in unit 18 contains an applanation lens 22 which, in the course of fixing the coupling-in unit 18, reaches the eye 10 for support on the surface of the cornea. The applanation lens has, on its side facing the eye, a contact surface designated by 24 in FIG. 1, which, in one embodiment, is designed substantially in a bidirectional adaptation to the actual contour of the human corneal surface. In this embodiment, the applanation lens 22 extends over the entire area of the cornea to be processed; she sits motionless on the cornea during the operation. In another embodiment, which is shown in dashed lines in Figure 1, the applanation lens is a rod lens, the contact surface is round-convex when viewed in a section transverse to the rod longitudinal direction. In particular, the rod lens may be a cylindrical lens, which extends in the direction of its longitudinal extent substantially rectilinear. In Figure 1, the rod lens is indicated at 22 '. Due to its comparatively small-area contact area with the corneal surface of the eye 10, it is movably arranged in the coupling-in unit 18, wherein a motor, for example electromotive or piezomotor, drive unit 25 is provided for driving the rod lens 22 ', which is driven by a suitable drive connection (indicated at 26). drivingly coupled or couplable with the rod lens 22 '.

Figure 2 shows the eye 10 in an enlarged view obliquely from the front. The cornea is indicated at 28. As a rule, its surface does not have an exact spherical contour, but rather an approximate bitoric shape. Bitterness means that the corneal surface runs along each of two main meridians that run transversely to one another aspherically, each with a different radius of curvature. The two meridians are shown in dashed lines in Figure 2 and designated 30, 32. In the human eye, the angle between the two meridians 30, 32 is often not exactly 90 degrees. Nevertheless, it has been shown that the human surface of the cornea can be mathematically well modeled by a bitorus surface with mutually perpendicular meridians. Accordingly, in the case of the bitoric applanation lens 22, the meridians of the contact surface 24 are preferably perpendicular to one another. It is certainly not excluded, for even better adaptation to the actual conditions of the human corneal surface, for example, depending on the particular patient, the meridians of the bitorischen contact surface 24 is not exactly perpendicular to each other, but for example at an angle of 85 degrees or another angle other than 90 degrees.

FIG. 3 schematically shows the applanation lens 22 in a state in which it is placed on the cornea 28 of the eye 10. The sectional view of Figure 3 shows the course of the contact surface 24 along the meridian larger radius of curvature. The rotated by 90 degrees sectional view of Figure 4, however, shows the course of the contact surface 24 along the meridian smaller radius of curvature. The asphericity of the contact surface 24 in the two meridian directions may be the same or different.

On its side facing away from the eye, the applanation lens 22 is shown in FIGS. 3 and 4 with a convexly curved shape. Other geometries of the eye-facing lens side of the applanation lens 22 are also possible. For example, in a modified embodiment, the eye-facing lens side of the applanation lens 22 may be a plane surface. Restrictions on the geometry of the eye-facing lens surface are by no means intended in the context of the invention.

The rod lens 22 'is shown enlarged in a cross-sectional view transversely to its rod longitudinal direction in Figure 5. Their eye-facing contact surface - now designated by 24 'to distinguish it from the bitoric contact surface 24 of the applanation lens 22 - is aspherically convexly curved and can be rectilinear or curved in the direction of the rod longitudinal direction of the lens 22 that is normal to the plane of the figure. In a straight longitudinal course of the contact surface 22, the rod lens 22 is a true cylindrical lens.

FIG. 6 illustrates how, by linear displacement of the rod lens 22 'transversely to its rod longitudinal direction along a displacement direction 34, a larger area of the cornea 28 can be swept over. It is understood that when moving the rod lens 22 'and the coupled into the eye laser beam (indicated in Figure 6 by a point 36) must be carried by appropriate control of the above-mentioned deflection so as not to the rod lens 22' passing directly into the Callus invade. If one wishes to machine the cornea 28 in a planar manner, the laser beam 36 can be moved back and forth along the longitudinal extension of the rod lens 22, ie transversely to the feed direction 34, by means of the deflection means, so that the laser beam 36 while the advancing movement of the rod lens 22 'continuously back and forth along the same. In this way, for example, it is possible to produce the areal depth cut in the cornea which is required for the flap preparation.

In contrast, FIG. 7 illustrates the rotational adjustment of the rod lens 22 '. Here it is rotated about the cornea 28 about a substantially central axis of rotation 38. If the laser beam 36 is held substantially at the same rotational axis offset longitudinal position of the rod lens 22 ', a circular cut 40 indicated by dashed lines can be generated.

Claims (6)

Laser device for ophthalmic surgery, comprising a laser radiation source (14) providing pulsed laser radiation and means (18) for coupling the laser radiation into an ocular treatment site, the coupling means comprising an applanation lens (22) to be placed on an ocular surface,
characterized in that the applanation lens (22) has an at least approximately bitoric contact surface (24) on its side facing the eye. Laser device for ophthalmic surgery, comprising a laser radiation source (14) providing pulsed laser radiation and means (18) for coupling the laser radiation into an ocular treatment site, the coupling means comprising an applanation lens (22 ') to be placed on an ocular surface,
characterized in that the applanation lens is designed as a rod lens and in that the applanation lens is associated with movement drive means (25, 26) for moving the applanation lens over the eye surface. Laser device according to claim 2,
characterized in that the movement drive means (25, 26) are arranged to move the applanation lens (22 ') transversely to its rod longitudinal direction substantially linearly over the eye surface. Laser device according to claim 2 or 3,
characterized in that the movement drive means (25, 26) are arranged to rotate the applanation lens about a lens vertical axis (38) to move the applanation lens (22 ') above the ocular surface. Laser device according to one of claims 2 to 4,
characterized in that the applanation lens (22 ') when viewed in a section transverse to the rod longitudinal direction has a convexly rounded contact surface (24') for engagement with the ocular surface. Applanation lens (22, 22 ') for use in a laser device according to one of the preceding claims, characterized in that it has an at least approximately bitoric contact surface (24) or a convex-cylindrical contact surface (24') on a lens surface intended for contact with an ocular surface. has.

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